1. Field of the Invention
The present invention relates to a magneto-resistance effect element and a magnetic memory.
2. Related Art
It has been proposed that a magneto-resistance effect element using magnetic films is used for a magnetic head, a magnetic sensor or the like, and is also used for a solid state magnetic memory (MRAM: Magnetic Random Access Memory).
In recent years, in a sandwiching structure film where a dielectric layer is interposed between two ferromagnetic layers, the so-called ferromagnetic tunnel junction element (Tunneling Magneto-resistance Effect element: TMR element) has been proposed as a magneto-resistance effect element utilizing a tunnel current obtaining by causing a current to flow in a film face perpendicularly thereto. Since a magneto-resistance change ratio (MR ratio) has reached 20% or more in the TMR element, there has been growing technical developments for public applications to MRAM.
The TMR element can be realized by, after forming a thin Al (aluminum) layer with a thickness of 0.6 nm to 2.0 nm on a ferromagnetic electrode, exposing a surface thereof to oxygen glow discharging or oxygen gas to form a tunnel barrier layer made from Al2O3.
A ferromagnetic single tunnel junction having a structure obtained by applying an anti-ferromagnetic layer to a ferromagnetic layer of the ferromagnetic single tunnel junction on one side thereof to make the ferromagnetic layer on the one side a magnetization pinned layer has been proposed.
A ferromagnetic tunnel junction including magnetic particles dispersed in dielectric and a ferromagnetic double tunnel junction (a continuous film) have also been proposed.
There is a possibility that these junctions are applied to the MRAM, because the magneto-resistance change ratio of 20% to 50% has been achieved and decrease in magneto-resistance change ratio can be suppressed even when a value of voltage applied to a TMR element is increased in order to obtain a desired output voltage value.
A magnetic recording element using the ferromagnetic single tunnel junction or the ferromagnetic double tunnel junction is non-volatile, and has a fast writing/reading time such as 10 nanoseconds or less and a potential that the number of rewriting times is 1015 or more.
Regarding a cell size of a memory, however, when an architecture where a memory cell includes one transistor and one TMR element is used, there is such a problem that the cell can not be reduced in size to a DRAM (Dynamic Random Access Memory) formed from semiconductor or smaller.
In order to solve this problem, a diode type architecture where a cell constituted of a TMR element and a diode connected in series are arranged between a bit line and a word line and a simple matrix type architecture where a cell constituted of a TMR element is arranged between a bit line and a word line have been proposed.
In both the cases, however, since reversion is performed by a current magnetic field due to current pulses at a time of writing in a storage layer, there is such a problem that power consumption becomes large, mass storage can not be achieved due to an allowable current density limit in wiring, and a driver area for allowing current to flow becomes large.
In order to overcome the above problem, there has been proposed a solid magnetic storage device where a thin film made from magnetic material with a high magnetic permeability is provided around a writing wire. According to such a magnetic storage device, since the magnetic film with a high magnetic permeability is provided around the writing wire, a value of a current required for information or data writing into a magnetic recording layer can be reduced efficiently. Even if such a storage device is used, it is very difficult to reduce writing current to 1 mA or less.
In order to solve these problems, a writing method utilizing a spin injection process has been proposed (for example, refer to U. S. Pat. No. 6,256,223). The writing method is constituted to utilize such a fact that magnetization of a magnetization free layer in a magneto-resistance effect element is spin-reversed by spin-injecting spin-polarized current into the magneto-resistance effect element.
In the writing method utilizing the spin injection, when spin injection is performed, annular magnetic field due to spin injection current is generated and spin reversion does not occur, when an element area is large. Therefore, an element with a small area is required.
Further, since high integration is required for application as a solid magnetic memory, it is necessary to form an element with a small area and with reduced area fluctuation.
As explained above, the spin injection process operating with a low writing current requires a formation of an element with a small area and also requires reduced area fluctuation for high integration.
In addition, in the spin injection process, when magnetization of a magnetic recording layer is reversed by injecting spin-polarized current, annular magnetic field due to the above current occurs in a memory element with a large area so that reversion of magnetization does not occur.
Since high integration is required for application as a solid magnetic memory, it is necessary to form an element with a small area and with reduced area fluctuation. Further, it is necessary to allow low current writing in cells with various sizes including a small cell with a size of 0.1×0.1 μm2 or less which is a limit for heat fluctuation resistance and provide heat stability of a magnetic recording layer to heat fluctuation. When the spin injection process is utilized, it is necessary to provide stability of magnetization in a magnetization pinned layer at a writing time.